Tropical rains breathe in sync with El Niño, the periodic warming of the equatorial Pacific Ocean. When the ocean is warm, wet zones contract; when it is cold, they expand. It is like an inhale and exhale, except the medium is water instead of air.
Scientists compared how much rain fell in the tropics during years with warm and cold phases. It turned out that during the transition from the warm phase to the cold phase, the probability of a year with less than 200 mm or more than 3000 mm of precipitation increases. During the reverse transition, it decreases. This is evident both in the numbers and on the maps: wet zones appear near South America or the Indian Ocean, while dry zones appear near Australia or Africa. Such a rhythm does not resemble gradual warming, because while temperatures rise, precipitation extremes alternately strengthen and weaken. This suggests that the ocean's natural seesaw may matter more than it seems.
The threshold for a 'dry' year in this work is 200 mm. For comparison, Moscow receives on average about 700 mm of precipitation per year, meaning a tropical point with 200 mm is three times drier than the Russian capital.